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Old 24th December 2013, 02:03 PM   #1
DHAA is offline DHAA  United States
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Default Hornresp Brainiacs - Help an Old Man

First off, I am an old man trying to learn some new tricks. After stumbling through WinISD and having a fairly successful build, I am moving on to embarrass myself with Hornresp. I have read many of the tapped horn build threads here and it is really amazing what you guys are doing.

So, I am trying to teach myself this program by reverse engineering some of the fine tapped horn cabs you young punks have already built. Are these following assumptions correct?

Using Hornresp, the S1-S5 values are AREA MEASUREMENTS at a particular point of the horn (the internal width of the horn multiplied by the depth of the horn at that point).

The L12-L45 are the actual measurements of the horn fold. They reflect the path the sound follows from the face of the speaker to the output of the cabinet.

If the previous assumption is correct, and I wanted to see the effect of making the cabinet slimmer, I would reduce each of these S1-S5 values proportionally to the new width of the cabinet. I would not alter the L12-L45 values at all.

EXAMPLE: If the cabinet I am studying has an internal width of 24" and I am attempting to model it with an internal width of 18", I would then reduce each S1-S5 values by 25% (18 divided by 24 = 0.75). I would then multiply the original S1-S5 values by 0.75 to see how the cab would model with an interior width of 18". I would not alter the L12-L45 values at all.

If the previous example is correct, then I could also use the same approach if I wanted to model making the cab wider.

EXAMPLE: If the cabinet I am studying has an internal width of 24" and I am attempting to model it with an internal width of 30", I would then increase each S1-S5 values by 25% (30 divided by 24 = 1.25). I would then multiply the original S1-S5 values by 1.25 to see how the cab would model with an interior width of 30". I would not alter the L12-L45 values at all.

So that is my question for today. Hopefully my understanding of this process is correct and my assumptions are true. If not, could one of you boy genius's help an old man out and try to help me understand what I am doing wrong?

Last edited by DHAA; 24th December 2013 at 03:14 PM.
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Old 24th December 2013, 03:38 PM   #2
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Your understanding of the parameters are correct, Merry Christmas, Old Man!

Art (old sound man) Welter
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Old 24th December 2013, 03:45 PM   #3
GM is offline GM  United States
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I’m 67, so not sure if I qualify as a ‘young punk’/’boy genius’ to you……………

Regardless, HR assumes a cylindrical aspect ratio, ergo the most correct conversion is to a square cross sectional area [CSA] ratio of the same area and as it increases to a rectangle, its accuracy declines with increasing aspect ratio to the point where this now ‘duct’ eventually becomes resistive enough in reality [~aperiodic around > 9:1] to no longer match up to the sim close enough to be of any value.

Consequently, getting the folds right severely limits the usable aspect ratios and why corner reflectors often hurt performance in higher aspect ratio designs. Ditto, ‘duct’ sections that act as acoustical resistors.

Both of course can be used to tailor a speaker’s response, just that HR can’t model them accurately.

GM
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Old 24th December 2013, 04:23 PM   #4
tb46 is offline tb46  United States
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H DHAA,

Take a look here:

Hornresp for Dum... hmm... Everyone - Home Theater Forum and Systems - HomeTheaterShack.com

and here:

Simple Tapped Horn Tutorial using Hornresp

That ought to keep you busy. :-)

As GM pointed out you have to get a feel for what may, or may not, work; and David McBean is in the process of adding additional functionality, I'm especially impressed w/ being able to see what stuffing does to the response.

Regards,
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Last edited by tb46; 24th December 2013 at 04:26 PM.
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Old 24th December 2013, 04:28 PM   #5
DHAA is offline DHAA  United States
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Thanks Art (old sound man) Welter and GM for your quick help. I guess I am not the only old man here! Let's just say I built my first cab over 30 years ago (when you had to do the heavy math yourself) and I really am liking these software cabinet modelers. After may years of inactivity, I have been building like a madman for the last six months and am really excited about the progress I have made. Thanks for coming to my "old man's roundtable." Would you like a beer with that?

GM - your comment about "HR assumes a cylindrical aspect ratio" seems to me to mean HR models the horn like it is a french horn. So any build with plywood will therefore never truly match HR's modeled predicted response. That is the first time I have heard that, thanks.

Then you commented "as it increases to a rectangle, its accuracy declines with increasing aspect ratio to the point where this now ‘duct’ eventually becomes resistive enough in reality [~aperiodic around > 9:1] to no longer match up to the sim close enough to be of any value."

How do you know when that happens? That is the first time I can remember hearing the term "[~aperiodic around > 9:1]". Is there a way to calculate that within HR, or is that something that requires deeper thinking and further calculation outside of HR?
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Old 24th December 2013, 04:47 PM   #6
DHAA is offline DHAA  United States
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Quote:
Originally Posted by tb46 View Post
H DHAA,

Take a look here:

Hornresp for Dum... hmm... Everyone - Home Theater Forum and Systems - HomeTheaterShack.com

and here:

Simple Tapped Horn Tutorial using Hornresp

That ought to keep you busy. :-)

As GM pointed out you have to get a feel for what may, or may not, work; and David McBean is in the process of adding additional functionality, I'm especially impressed w/ being able to see what stuffing does to the response.

Regards,

TB46 (Olliver), thanks for those links. I had actually stumbled upon the "Hornresp for Dummies" once before, but that was at the beginning of quest and I was sub-dummy at that point. I think I have gained enough knowledge now that if I reread that again and it may make more sense. I had forgotten about that link, so thanks for your post.

I don't think I have seen the "Simple Tapped Horn Tutorial" before though. I have to sit here at my desk all day, with nothing to do since it is Christmas Eve, so I should be able to read both of those posts in their entirety today.

Are you an old man too, or a boy genius doing some community service?

Last edited by DHAA; 24th December 2013 at 05:07 PM.
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Old 24th December 2013, 06:46 PM   #7
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Quote:
Originally Posted by DHAA View Post
GM - your comment about "HR assumes a cylindrical aspect ratio" seems to me to mean HR models the horn like it is a french horn. So any build with plywood will therefore never truly match HR's modeled predicted response. That is the first time I have heard that, thanks.
Cylindrical like a french horn (or any other musical horn) that's round and straightened out (no bends) and with all the holes closed.

The Hornresp predicted response will never exactly match reality because there's a multitude of things Hornresp does not account for. I can post a long list if you like. But the Hornresp sim will still be remarkably accurate. You just have to know what's involved in the differences between a simulation and reality.

Quote:
Then you commented "as it increases to a rectangle, its accuracy declines with increasing aspect ratio to the point where this now ‘duct’ eventually becomes resistive enough in reality [~aperiodic around > 9:1] to no longer match up to the sim close enough to be of any value."

How do you know when that happens? That is the first time I can remember hearing the term "[~aperiodic around > 9:1]". Is there a way to calculate that within HR, or is that something that requires deeper thinking and further calculation outside of HR?
As the aspect ratio increases past 1:1 things change, but I think "no longer match up to the sim close enough to be of any value" is a bit harsh at 9:1. Unless you want to build a complex throat like the Labhorn, simple construction methods dictate that you will have a fairly large aspect ratio at the throat, especially with very small throats (high compression ratios). The highest throat aspect ratio I ever built was almost 20:1. (Compression ratio was a bit more than 5:1, SD:S1. Hornresp defines compression ratio as SD:S2 for offset driver horns and this horn was offset, so by Hornresp's calculation the compression ratio was a lot less than 5:1.) And the measurement was still reasonably close to the sim, all things considered. No worse match between sim and measurement than anything else I've built anyway. I didn't measure at high power though, and that might have changed things since the Reynolds number increases with velocity.

Last edited by just a guy; 24th December 2013 at 06:53 PM.
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Old 24th December 2013, 06:46 PM   #8
tb46 is offline tb46  United States
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Hi DHAA,

On the risk of plagiarism I'll steal GM's line (Post #3): "I’m 67, so not sure if I qualify as a ‘young punk’/’boy genius’ to you……………" It fits. I will try to do a little community service once in a while, even though lately "they" have not been able to make up their mind if they want to chain me to the sodering iron or the computer (hint: noticed the oil price?). Today I'm having a little bit of slack, then back to family duty. :-)

Regards,
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Old 25th December 2013, 05:36 PM   #9
DHAA is offline DHAA  United States
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Default Question of the Day - Compression Ratio

Just a Guy, thanks for your comments, and you actually brought up my next question.

What I am experimenting with right now is to taking proven tapped horn designs and narrow/widen them to see how it affects response. I am trying to gain a deeper understanding of how all these different design parameters affect each other. But if I am understandg compression ratio correctly, narrowing/widening the cabs would also directly effect the compression ratio (SD divided by S2).

- I see no way within HR to check compression ratio - I assume you calculate it independently?

- When you design a tapped horns, how do you know what the best compromise for compression ratio is?

- What are the dangers to look for in regards to compression ratio.

- What exactly are the effects of raising/lowering the compression ratio? Is it apparent is the HR modeled frequency response at all, or does compression ratio more affect safeguarding the driver from self destruction?

Thanks everyone for your help so far. Uuuuuummmm, I smell ham cooking - I better get downstairs before it disappears. Merry Christmas to all, and to all a good tapped horn!

Last edited by DHAA; 25th December 2013 at 05:45 PM.
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Old 25th December 2013, 06:16 PM   #10
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Quote:
Originally Posted by DHAA View Post
narrowing/widening the cabs would also directly effect the compression ratio (SD divided by S2).
Only if you narrow/widen the throat area. You can do whatever you like to the rest of the horn and it won't affect compression ratio. And compression ratio is SD:S2 only for tapped horns and offset driver horns. Compression ratio for end loaded horns is SD:S1.

Quote:
- I see no way within HR to check compression ratio - I assume you calculate it independently?
For an end loaded horn, hover the mouse pointer over the S1 box and at the bottom of the Hornresp screen it will tell you the compression ratio. For an offset driver horn or tapped horn, hover the mouse pointer over the S2 box and at the bottom of the Hornresp screen it will tell you the compression ratio.

Quote:
- When you design a tapped horns, how do you know what the best compromise for compression ratio is?
You can use math to figure out the best throat area but that is more advanced than most people are capable of. Instead, most people just play around with the sliders until they get the response they want. A throat area of 3:1 (SD:S1) is usually considered safe. Going beyond 3:1 may have negative effects in a bunch of different areas.

Quote:
- What are the dangers to look for in regards to compression ratio.
It's going to affect aspect ratio of the throat unless you use fancy geometric shapes in your construction to keep the throat square shaped. It's going to affect pressure on the cone and too much pressure could damage the driver at high power. It's going to affect velocity of air and too much velocity could introduce turbulence at high power.

Quote:
- What exactly are the effects of raising/lowering the compression ratio? Is it apparent is the HR modeled frequency response at all, or does compression ratio more affect safeguarding the driver from self destruction?
A higher compression ratio will need a longer horn to maintain the same tuning. A longer horn is a bigger horn. A bigger horn will be louder. At the same time, it can be a lot easier to get a very flat response (without huge peaks and valleys) from a very small throat, but that's not always the best thing to do because a very small throat introduces other issues as I've explained previously in this post and the last one.

Changing the throat size is VERY apparent in the frequency response. But at the same time, it depends how much of the horn changes when you change the throat size. If L12 is very short and you just change S1 there won't be much change in the sim (and this won't actually change the reported compression ratio of a tapped horn). But if L12 is very long, or if S2 is set to auto the changes will be much more noticeable (and this will change the reported compression ratio of a tapped horn).

It can change things enough that other areas of the horn need to be adjusted to maintain the same tuning and response curve shape.

Anyway, I could type a book here and it wouldn't do you nearly as much good as just getting a few minutes of experience with Hornresp. Play with the sliders and see what happens. When you get something that looks good post it up and we'll let you know if there are any problems.

Last edited by just a guy; 25th December 2013 at 06:24 PM.
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